Fig. 4From: Machine learning methods to predict the cultivation age of Panacis Quinquefolii Radix3D surface plots of A the number of samples in the test sets that fall within the AD (IDs) as a function of k and Z; and B–E the negative value of MSE predicted by the four ML models for the test samples within the AD as a function of k and Z. k = 6 and Z = 1.6 (black dot in each figure) are chosen to define the AD for all modelsBack to article page